It is known in the electronics industry to use busbars to make electrical connections between various components. In the context of batteries, busbars may be used to join multiple battery cells in a desired series or parallel configuration to create the desired electrical properties of a battery module or battery pack.
Battery systems may be used to provide power in a wide variety of applications. Examples of transportable applications include hybrid electric vehicles (HEV), plug-in HEVs, and electric vehicles (EV). Examples of stationary applications include backup power for telecommunications systems, uninterruptible power supplies (UPS), and distributed power generation applications.
Busbars provide the electrical connection between cells and between modules. Busbars require a conductive material, originally copper, shaped in a geometry that can connect at least two cell terminals or at least two module terminals. Busbars are usually welded or fastened to the cell terminals. Welding requires a robust automated process with numerous quality control measures in place. Fastening is a very time-consuming process when a pack has thousands of cells, typically with at least two fasteners used for each cell.
Examples of the types of batteries that are used include nickel metal hydride (NiMH) batteries, lead-acid batteries, lithium batteries, lithium-ion batteries, and other types of batteries in a cylindrical form factor. A battery module includes a plurality of cells that are connected in series, parallel, or a combination thereof. The modules themselves may be connected in series, parallel, or a combination thereof in forming a complete battery pack.
One common challenge with designing busbars is the avoidance of an electrical short. An electrical short is the application of a cell or module voltage on a feature with very low resistance. This results in very high current, leading to rapid heating of the circuit. If the battery cell comprises electrolyte or chemicals that expand during heating, shorting of some cells may cause venting of gases or rupture of the cell casing. Igniting of the gases or the heated internal elements of a shorted cell may cause a thermal event. Often, a chain reaction ensues, wherein a violent reaction of one cell to a short may propagate to other nearby cells, thus causing a catastrophic consequences.
Even in typical operation, cells produce heat as they are being charged and discharged. If the heat is not dissipated in time, the cell may reach temperatures that can cause similar effects as described for a shorted cell.
Welded and fastened busbars can easily accommodate a fusible link. Some designs in the art rely on solder fuses from the busbar to each cell, which is time-consuming and expensive. Moreover, traditional pressure-based busbar cannot use soldered fuses.
Further, busbars are typically not part of the cooling design, although they are on the shortest path for the heat created in the cells to be removed.
The present invention is directed to overcome one or more of the problems as set forth above.